This invention relates to a novel chlorinated polyolefin elastomer having unique physical characteristics and to a process for making the same.
The chlorinated polyolefins, i.e., chlorinated polyethylene and chlorosulfonated polyethylene, have rubber-like properties due to the substitution of chlorine atoms into the polyethylene. These elastomers are resistant to deterioration due to ozone, they are resistant to solvents and they have a high resistance to the swelling action of oils. Chlorosulfonated polyethylene has sulfonyl chloride groups in the elastomer and these groups provide sites of reactivity through which crosslinking or curing, if desired, can be effected.
Chlorinated polyethylene and chlorosulfonated polyethylene elastomers have been used to coat fabrics to make tarpaulins, to make industrial pump diaphragms, to make conveyor belts, for wire and cable jacketing, and, more recently, they have been used as pond and pit liners, and roofing film. The uncured elastomers are sold as such and usually they are subsequently compounded with acid acceptors, pigments, fillers, and the like, and formed into products by, for example, calendering or extrusion processes. These chlorinated polyethylene elastomers can also be cured by conventional procedures. Prior to the present invention, when chlorinated polyethylene elastomers were formed, especially when the elastomer was calendered or extruded, it was very difficult to feed the uncured compounded elastomer into the equipment, for example, the nip of the counter-rotating calender rolls, so that the rollers or other feeding mechanism would readily pick up the uncured compounded elastomer to form a finished product. More importantly, when extruding the compounded chlorinated polyethylenes known prior to the present invention into sheets or films it was not possible to substantially draw down the sheets or films to reduce their thickness without rupturing them. The present invention provides a chlorinated polyethylene elastomer that can be substantially drawn down without rupturing or breaking to make a wider range of thickness of sheets or films.
Prior to the present invention in order to make an elastomer that processes more readily and shows an improvement in elongation, it was necessary to add to the elastomer rather large amounts of plasticizer and to use higher temperatures when calendering. The addition of plasticizers in amounts sufficient to improve elongation adversely affects the properties of the elastomer. In addition, if the temperatures used during the calendering operation are increased, for example, to about 150.degree.-165.degree. C. when processing chlorosulfonated polyethylene, in order to sufficiently lower the viscosity of the chlorinated polyethylene elastomer for ease of processing, the elastomer starts to decompose. Furthermore, such temperatures increase the potential for SO.sub.2 evolution and scorching, i.e., premature vulcanization.
The present invention provides a novel uncured chlorinated polyethylene elastomer that has valuable characteristics of other chlorinated polyethylenes, but, in addition, the uncured elastomer is easily processible and, quite surprisingly, the elastomer even when compounded can be elongated substantially more than known chlorinated polyethylene elastomers without rupturing or breaking.